Automatic operating point control system



Aug. 11, 1942- w. DILLENBURGEIR 2,292,369 I AI J TOMATIC OPERATING POINT CONTROL SYSTEM Filed Oct. 9, 1940 //v l/EN TOR W DILLENBURGER A T TORNEV Patented Aug. ll, 1942 NET!) STATE s PATENT OFFICE AUTOMATIC OPERATING POINT CONTROL SYSTEM Wolfgang Dillenburger, Kleinmaclmow, near Berlin, Germany assignor to Fernseh G. m. b. IL,

Berlin-Zelilendori, Germany Application October 9, 1946, Serial No. 360,417

In Germany October 19, 1939 6 Claims.

The invention relates to circuit arrangements and in particular to modulating circuits having a V-shaped grid voltage output current curve.

It is an object of the invention to provide a Fig. 1 shows a circuit arrangement according to the invention and Fig. 2 a diagram of the grid voltage output current characteristic curve of the circuit of Fig. 1.-

The multigrid tubes I and 2 of Fig. l are arranged in a bridge circuit.- The grids 3 and 4 are connected to a source 5 of carrier frequency.

v The bridge circuit is 50 adjusted that the high prove systems in which the operating point is adjusted by hand, for instance, by changing a control voltage of the tubes used for producing the -V-shaped characteristic.

A suitable curve can be obtained, for instance, by two amplifier tubes arranged in a bridge circuit or by a parallel arrangement of two tubes. The invention has an important field of use in modulating circuits for television purposes in which the carrier shall'have a well defined value and in which the carrier is modulated from this fixed value. In such cases it is necessary to operate at the lowest point of the V-shaped grid voltage output current curve if the modulated signals shall be given as amplitudes passing beyond this fixed value which may or may not be the black value.

According to the invention one or the other of two voltages of opposite phase are produced in case the operating point is moving in the direction of one or the other branch of the grid voltage output current curve. These voltages are utilized for controlling the arrangement so that the operating point is kept at the lowest point of the curve. The control voltage may, for instance, be produced by superposing the high frequency voltages appearing in the output when 1 the operating point does not coincide with the lowest point of the curve upon an auxiliary constant high frequency'carrier having an equal or counter phase and utilizing the resulting voltage after rectification for adjusting automatically the operating point, for instance, by controlling the grid of one of the tubes of the arrangement. The auxiliary constant high frequency carrieris preferably the carrier frequency employed in the modulating circuit.

' Other aspects of my invention will be apparent or will be specifically pointed out in the description forming a part of this specification, but I do not limit myself to the embodiment of the invention herein described, as various forms may be adopted within the scope of the claims.

l-teferring to the drawing frequency oscillations are essentially compensated in the output transformer 6, I. The grid 8 of tube I is connectedto a source 9 of modulating signals. If no modulating signals are applied to grid 8 the output current at the terminals III and II will be zero or a minimal value of the carrier oscillations when the bridge-is correctly adjusted. When the adjustment is changed, for instance, by changes in temperature or by changes of the current supply the arrangement does not operate any more at the lowest point of the grid voltage output current curve. This curveris represented in Fig. 2 in which u; represents the grid voltage and L the amplitude of the output current at terminals I0, I I. The point A is the working point which shall be kept constant. If the operating point moves either towards the right or left side a larger value of the carrier will be present in the output circuit III, II. The anode currents of tubes I and 2 are then no more equal so that the compensationin coil I cannot take place. If the operating point moves in the direction of the right branch of the curve a carrier oscillation will be produced in the output circuit which is in opposite phase to that produced in case the operating point is moving in the direction of the left branch of the curve. These oscillations of opposite phase are utilized for producing a control voltage. The oscillations are supplied by way of a tube I2 and a transformer I3 to a tube II. A grid I6 of this tube is connected by a line I5 to the source of carrier frequency 5. This carrier frequency has a constant phase and amplitude so that by superposition with an oscillation of equal or opposite phase respectively a larger or smaller value of the output current is produced in the anode circuit of a tube II. The anode of this tube is connected by way of a transformer to a diode II for rectifying the output oscillations. The rectifled voltage is applied by way of a line It to the grid I9 of tube 2. This tube is influenced thereby in such a manner that the control voltage counteracts a further rise of the high frequency in the output of the bridge circuit so that the device is keptautomatically at point A of the curve of Fig. 2. The elements for'producing the control voltage must be in operation when the modulating voltage has its zero value 1. e. when the bridge circuit is balanced. In order to secure a correct'operation the tube'l2 can be influenced additionally by control impulses at grid 20.. This grid is connected to a source 2| of conv trol impulses which are, for instance, similar to way of line I5 must always have one and the same amplitude for a correct operation of the device and it may therefore be preferable to arrange special means between the source of carrier oscillations 5 and grid l6 for keeping the amplitudes at a constant value.

It may be "desirable under certain operating conditions that even if the circuit is operating at the lowest point of the curve of Fig.2 a small value of high frequency energy remain. This remaining high frequency amplitude may however be kept very small, for instance, below 1%. The controlling oscillations may be amplified if necessary so that a controlling action of sufficient sensitivity is obtained. It may also be preferable to adjust the phase of the high frequency oscillations applied to tube It by a phase adjusted.

The invention can be employed generally in circuit arrangements having a V-sh aped grid voltage output current curve. It is however of particular advantage in arrangements for the modulating of television transmissions in which a fixed value for the carrier amplitude shall be used. If no modulating signals are present the amplitude of the carrier wave shall be practically zero or have a certain fixed value, and this fixed value must always be kept constant. This fixed value of carrier frequency amplitude is present at certain well defined intervals when the modulating television signal has a certain datum potential representing black tone value, for example, 'so that the automatic adjustment of the bridge circuit may take place at these intervals. The circuit arrangement particularly the rectifier with the diode H has a time constant of such magnitude that the automatic ad- Justment remains eflective during the time lying between the control intervals.

The embodiment represented in Fig. 1 is shown by way of example and the invention is not limited thereto. The invention can be employed in connection with other types of circuits having a characteristic curve corresponding to Fig. 2, for instance, in circuits in which the carrier .frequency is applied to two parallel tubes one of which has a positive and the other of which has a negative slope. In this case the modulating frequency controls theslope of one of the tubes. The controlling action is effected in a manner similar to that of Fig. 1.

What I claimis:

1. An arrangement for automatically adjusting the operating point on its characteristic curve of a balanced bridge modulator which comprises means for producing an electromotive force of a certain value when theamplitude of the output current of said modulator is'zero, means for increasing said electromotive force in response to modulator output current of a certain phase and for decreasing said electromotive force'in response to modulator output current of a different phase, and means for applying said electromotive force to said modulator to maintain the output current of said modulator at a desired fixed amplitude when the modulating signal has a certain amplitude which may be zero.

2. Modulating apparatus comprising a first and a second electric discharge device each having an anode, a cathode and a control means comprising at least one control electrode, an output circuit, a transformer for coupling said output circuit to the anode-cathode circuits of said electric discharge tubes, a source of carrier current, means for impressing a carrier frequency electromotive force from said source upon the control means of said electric discharge devices, a source of varying modulating electromotive force having a periodically recurring fixed amplitude, means for impressing said modulating electromotive force upon the control means of the first electric discharge device to produce a' modulated carrier electromotive force in said output circuit, means operative periodically only at times when said modulating electromotive force has said recurring fixed ampli-.

tude for producing impulses of carrier electromotive force under control of and corresponding to the modulated carrier electromotive force in said output circuit, means under joint control of said impulses of carrier electromotive force and unmodulated carrier electromotive force'from said source of carrier current for producing a current which varies in accordance with a characteristic of said impulses of carrier electromotive force, means for producing under control of said last-mentioned current a unidirectional electromotive force having variations rent circuits a current having a carrier frequency 4 y component, means for applying a modulating electric discharge device of said pair, and means effective only when the modulating electromotive force has a predetermined amplitude for increasing said control electromotive force in response to an amplitude increase in the carrier component of the anode current in the anode current circuit of one of said electric discharge devices and for decreasing said control electromotive force in response to an increase in the carrier component of the anode current in the anode current circuit of the other of said electric discharge devices.

4. A balanced bridge modulator comprising a pair of electric discharge devices, an output circuit for said modulator, means for applying a carrier electromotive force to said modulator, means for applying a modulating electromotive force to said modulator to produce in said output circuit a carrier current modulated in accordance with said modulating electromotive force, means for applying a control electromotive force to said modulator, and means effective only when the modulating electromotive force has a predetermined amplitude for increasing said control electromotive force in response to carrier current in said output circuit having a predetermined phase relationship with respect to the carrier electromotive force applied to said modulator and for decreasing said control electromotive force in response to carrier current in said output circuit having a different phase relationship with respect to the carrier electromotive force. 1

5. A balanced bridge modulator comprising electric discharge means having two anode current paths, a source of carrier current for said modulator, means for applying a modulating electromotive force to said modulator to cause one only of the anode currents in said paths to vary in accordance with signals thereby causing the production" of a signal modulated carrier current in the output circuit of said modulator, and means responsive to said output carrier cur- 6. A balanced bridge modulator comprising electric discharge means having two anode current paths, a source of carrier-current for said modulator, means for applying a modulating electromotive force to said modulator to cause one only of the anode currents in said paths to vary in accordance with signals thereby causing the production of a signal modulated carrier current in the output circuit of saidmodulator, and means responsive to said output carrier current only at intervals during which said modulating electromotive force has a .fixed datum amplitude for controlling'the amplitude of the carrier current in the other of said anode current paths to maintain substantially constant the ratio of said anode currents during said intervals.

WOLFGANG DILLENBURGER. 

